On a griddle or saute pan, heat oil on medium-high heat. Season steak and saute for 6 to 8 minutes flipping constantly. Add the onion the last minute of cooking into the same pan. Add lime juice and remove from the heat.

Split the bread lengthwise and cut into 4 pieces. Coat bread pieces with mayonnaise on the top side. On the bottom side, layer tomatoes, lettuce, steak, onions, and shoestring potatoes. Serve hot.